Classic slicing error with thin wall. Rule #1 always preview your gcode when a print has critical thin walls. You would have seen this gap without ever printing it.#2 Adjust the number of shells when doing thin wall object, and again, be conscience of a slicing issue where if the number of shells exceeds the space between the 2 walls then the slicer assumes that space was taken by shells and does not go back and attempt infill.Ideamaker does have settings you can attempt to adjust and see if it fills in the gap.

FWIW, gaps not filled between a thing wall structure has been one of the longest standing repeated errors since I started 3D printing back in 2009. Here is an example topic and discussion, about the time some of these new "gap filling" features and settings were added to ideamaker.viewtopic.php?f=3&t=4154&p=22534&hilit=thin+wall+gap#p22541